Single herbal medicine for diabetic retinopathy (Review)

Methodological quality of the review: High confidence

Author: Zhang HW, Zhang H, Grant SJ, Wan X, Li G

Region: China and Poland

Sector: Diabetic retinopathy

Sub-sector: Herbal medicine

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Diabetic retinopathy is one of the major causes of blindness and the number of cases has risen in recent years. Herbal medicine has been used to treat diabetes and its complications including diabetic retinopathy for thousands of years around the world. However, common practice is not always evidence-based. Evidence is needed to help people with diabetic retinopathy or doctors to make judicious judgements about using herbal medicine as treatment.

Objectives:

To evaluate the effectiveness and harm of single herbal medicine for diabetic retinopathy.

Main findings:

In total, authors included 10 randomized controlled trials (RCTs)  in the review. Nine of the 10 studies were conducted in China and one was conducted in Poland. Authors note that in all studies, participants in both groups received conventional treatment for diabetic retinopathy which included maintaining blood glucose and lipids using medicines and keeping a stable diabetic diet. In three studies, the comparator group also received an additional potentially active comparator in the form of a vasoprotective drug. The single herbs or extracts included Ruscus extract tablet, Sanqi Tongshu capsule, tetramethylpyrazine injection, Xueshuantong injection, Puerarin injection and Xuesaitong injection. The Sanqi Tongshu capsule, Xueshuantong injection and Xuesaitong injection were all made from the extract of Radix Notoginseng (San qi) and the main ingredient was sanchinoside. The risk of bias was high in all included studies mainly due to lack of masking (blinding). None of the studies reported the primary outcome of this review, progression of retinopathy.

Authors report that combined analysis of herbal interventions suggested that people who took these herbs in combination with conventional treatment may have been more likely to gain two or more lines of visual acuity compared to people who did not take these herbs when compared to conventional intervention alone at the end of treatment (RR 1.26, 95% CI 1.08 to 1.48; five trials, 541 participants; low-certainty evidence). Subgroup analyses based on the different single herbs found no evidence for different effects of different herbs, but the power of this analysis was low. One study reported Sanqi Tongshu capsule might be associated with a greater reduction in microaneurysms and haemorrhages in the retina (very low-certainty evidence). The pooled analysis of two studies on tetramethylpyrazine or Xueshuantong injection showed such herbs may have had little effect on lowering HbA1c (MD 0.00, 95% CI -0.58 to 0.58; 215 participants; low certainty evidence).

There was very low-certainty evidence on adverse events. Two studies reported minor adverse events such as uncomfortable stomach, urticaria, dizziness and headache. There was no report of observation on adverse events in the other studies.

Authors note that no conclusions can be drawn about the effect of any single herb or herbal extract on diabetic retinopathy from the evidence gathered in this review.

Methodology: 

Inclusion criteria consisted of RCTs and quasi-RCTs that have investigated the effects of any single herb (or extracts from a single herb) as a treatment for people with diabetic retinopathy. Authors considered the following comparators: placebo, no treatment, non-herbal (conventional) medicine or surgical treatment.

Authors conducted a search on CENTRAL, which contains the Cochrane Eyes and Vision Trials Register,MEDLINE, Embase, OpenGrey, the ISRCTN registry, ClinicalTrials.gov and the ICTRP. The date of the search was 12 June 2018. They also searched the following Chinese databases in June 2013: Chinese BioMedical Literature Database (CBM), Traditional Chinese Medical Literature Analysis and Retrieval System (TCMLARS), Wanfang China Dissertation Database (CDDB), Wanfang China Conference Paper Database (CCPD) and the Index to Chinese Periodical Literature. Authors also reviewed reference lists of included studies.

Two authors screened studies for inclusion, extracted data and assessed the quality of included studies. Authors conducted a meta-analysis using risk ratio for dichotomous outcomes and mean differences for continuous outcomes, with 95% confidence intervals. Certainty of evidence was assessed using GRADE.

Applicability/external validity:

Authors state that they cannot conclude the effect of herbal medicine on diabetic retinopathy.

Geographic focus:

The combined analysis of eight studies, which were conducted in did not provide substantial evidence to support or refute the use of any herb or herbal extract in people with diabetic retinopathy.

Summary of quality assessment:

Overall, there is high confidence in the conclusions about the effects of this study. Authors used rigorous methods to search, scree, extract data and assess the quality of included studies. Authors did not draw strong conclusions based on the included evidence and appropriately addressed limitations of the review.